The present invention relates generally to improvements in single lens reflex cameras provided with through the lens light measuring systems and it relates more particularly to an improved TTL light measuring single lens reflex camera of the type provided with interchangeable objective lens of the fully open and stopped down aperture light measuring types, and to an improved mechanism for inhibiting and indicating the improper selection of a stopped down light measurement mode with the use of an objective lens of the fully open aperture light measuring type.
In single lens reflex cameras of the TTL light measuring type, when the light is measured with a full aperture light measuring type objective mounted on the camera, the indication on the exposure control meter often differs in a full aperture light measurement from that in a stop-down light measurement depending on the error derived from converting the F-value obtained in the full aperture light measurement into an electric resistance, or on the difference between the indicated F.sub.NO and real F.sub.NO. It has been almost impossible to practically precisely coincide these. The difference in the exposure control meter indication between the full aperture light measurement and the stop-down light measurement confuses and perplexes the photographer and leads to errors in photographing operation.